Crucible of refractory semi-conductive material



Nov. 15, 1960 BLOK 2,960,326

CRUCIBLEI OF REFRACTORY SEPJlI-CONDUCTIVE MATERIAL Filed Nov. 19, 1957 INVENTOR LDURENS BLOK AGE United States Patent i CRUCIBLE 0F REFRACTORY SElVII-CONDUCTIVE MATERIAL Lourens Blok, Eindhoven, Netherlands, assignor to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Nov. 19, 1957, Ser. No. 697,361

Claims priority, application Netherlands Nov. 20, 1956 ZClaims. (Cl. 263-48) This invention relates to elongated crucibles of refractory semi-conductive material such as graphite. Such crucibles may be employed for melting and, if desired, purifying materials by the methods known per se under the names Zone-levelling or zone-refining (see, for example, US. Patent No. 2,739,088). In these methods, the crucible is preferably moved through a high-frequency inductance coil, so that the heat produced in the semi-conductive material of the crucible and, as the case may be, in the material contained therein is sufficient to fuse the melting material.

Known crucibles, which on account of their elongated form are better known under the name boats, have the disadvantage that the heat produced therein by a highfrequency field is greater at their extremities than at the centre so that non-uniform heating of the melting material occurs, which, for reasons which are not important for the present invention, is undesirable.

The invention underlies recognition of the fact that this effect is attributable to the cross-sections of such boats being larger at their extremities than in the remaining portion, so that the eddy-currents induced in the boat are greater at its extremities.

According to the invention, the underside of the boat, at least at one extremity, contains one or more recesses such that the cross-section of the material at this extremity is constant. Although such a step is usually taken at each extremity, this is not always necessary since in known methods it often sutfices if a constant production of heat is obtained at only one end.

In order that the invention may be readily carried into effect, one embodiment will now be described more fully, by way of example, with reference to the accompanying drawing, in which:

Fig. l is a side-view of a boat according to the invention, and

Figs. 2 to 4 are cross-sectional views, taken along the lines IIII, IIIIII, and IVIV, respectively, in Fig. l.

The boat 1 as shown in Fig. 1 is formed from a circular rod of graphite, in which first a central portion 2 of segment-shaped section, which is shown in dotted line in Fig. 2, was removed by milling and then an elongated cavity 3 was provided by milling.

As may be seen from Fig. 3, a similar segment-shaped portion 4 was removed by milling at the lower side near the extremity or end and then a groove 5 was provided, so that the solid cross-section at this area is inverse to, or a flat-mirror image of, that of the central portion of the boat and therefore substantially the same. This resulted in lugs =6 being formed, which may be connected This leads to a variation in cross-section, but this is too 2,960,326 Patented Nov. 15, 1960 far remote from the melting material to cause any difficulty. Furthermore, the current source is usually switched oif already if this end is coupled to the highfrequency coil. This coil 8 is shown diagrammatically in Fig. 1.

Partitions 9 of the boat, one of which is shown in section in Fig. 4, are provided between the sections II and III. By careful shaping thereof it may readily be achieved that the heat induced at these areas is equal to that produced at the centre of the boat.

It will be evident that several variations in the shape of the cavities to be provided at the underside of the crucible are possible within the scope of the invention.

What is claimed is:

l. A crucible of refractory semi-conductive material comprising an elongated, material-holding, middle section having generally vertical side walls and generally vertical end walls and a longitudinal axis and contiguous therewith and separated therefrom by an end wall a non-material-holding end section, said material-holding middle section having along substantially its entire length a uniform substantially U-shaped cross-section transverse to its axis and possessing a uniform cross-sectional area throughout its solid portions, said end section having a recess at a lower portion thereof and a transverse crosssectional area of its solid portions at the recessed portion substantially the same as that along substantially the entire middle section, the portion of the crucible intermediate the middle section and the said one end section having a transverse cross-sectional area of its solid portions substantially the same as that along substantially the entire middle section, whereby more uniform heating of material in the crucible by high-frequency currents is obtained.

2. A crucible of refractory semi-conductive material comprising an elongated, material-holding, middle section having generally vertical side walls and generally vertical end walls and a longitudinal axis and contiguous therewith and separated therefrom by an end wall opposed non-material-holding end sections, said material-holding middle section having along substantially its entire length a uniform substantially U-shaped cross-section transverse to its axis and possessing a uniform cross-sectional area throughout its solid portions, one of said end sections having an axially-extending recess at a lower portion thereof and a transverse cross-section of its solid portions thereat that is a flat-mirror image of that of the middle section and a transverse cross-sectional area of its solid portions at the recessed portion substantially the same as that along substantially the entire middle section, the section of the crucible intermediate the middle section and the said one end section having a channelled cross-section whose transverse cross-sectional area of its solid portions is substantially the same as that along substantially the entire middle section, whereby more uniform heating of material in the crucible by high-frequency currents is obtained.

References Cited in the file of this patent UNITED STATES PATENTS 2,593,015 Dreher Apr. 15, 1952 2,615,060 Marinace et al. Oct. 21, 1952 2,776,131 Marino Jan. 1, 1957 FOREIGN PATENTS 1,695 Great Britain Apr. 21, 1904 

